A wide variety of separators have been developed that separate and accumulate various objects transported by an air stream, such as paper waste, scrap material, food items, or other products. These separators utilize various configurations which are designed to receive a high velocity stream of air transporting prescribed objects, and subsequently separate the objects from the conveying air. The objects are typically accumulated at or near a designated exit, while the air or other transport gas is directed to a second exit. A problem associated with many separating systems, and particularly in separating systems design for the collection of scrap paper, is that they typically generate a large amount of dust and/or other air-borne contaminants proximate the material exit.
One type of separator that has been extensively used is a cyclone separator wherein the transported objects and a stream of air are introduced into a large cylindrical or cone-shaped device. The transported objects are introduced into the cylindrical housing so that they are thrust against the outer wall by centrifugal forces resulting from the flow of the air stream within the cylinder. The air exits via the top of the cylindrical device while the objects are typically funneled out a bottom exit. Cyclone separators are generally very large and somewhat expensive pieces of mechanical equipment. Cyclone type separators are often so large that it is not feasible to install them inside a building. Consequently, most cyclone type separators are typically situated outside the building and often on the roof of the building. Reducing the dust in these exterior cyclone separators has not been of great concern because the presence of dust outside a building typically does not adversely affect people or equipment.
A prior art cyclone separator system that is concerned with the separation of dust from the transported objects is disclosed in U.S. Pat. No. 3,116,238 issued to Van Etten. The '238 patent discloses a modified cyclone type separator that includes the standard central air discharge funnel directing the air from the cyclone separator. It also includes a screen disposed along the outer wall of the separator to facilitate the separation of removal dust and fine particles from the stream of air and conveyed material. While this device attempts to address the problem caused by dust associated with the separating action, there remain several other problems associated with this patented device. Namely, it is still a very large device, and the air maintained within the housing is maintained at a high velocity and thus a relatively high static pressure.
Another type of separator is a tangential separator where the transported objects are recovered on a flat or cylindrical screen and the air which passes through the screen exits the separator in a generally tangential orientation. Tangential separators are typically smaller devices than the cyclone separators and thus are often installed within the confines of a building or factory. For this reason, the air exiting the tangential separator is typically reintroduced into the interior environment of the building or is reused within the air conveying system. In either situation, it becomes increasingly important to filter the exiting air prior to its reuse and to minimize the dust and other contaminants introduced into the environment near the material exit.
Most applications in which tangential air separators are used can be classified either as a positive ("upush type") system, a draw through ("pull type") system, or a hybrid system. As the classification suggests, draw through or "pull type" systems are those in which the air stream and transported objects are pulled into the separator with a fan located downstream of the separator. In such draw through systems, the separator is typically maintained below atmospheric pressure and typically requires an air lock to prevent any back flow of air from the object discharge exit. Positive or "push type" systems, on the other hand, include systems where the air and conveyed objects are blown into the separator with the fan located upstream of the separator. In push type systems, the pressure within the separator is above standard atmospheric pressure. The hybrid systems involve both "pushing" as well as "pulling" of the conveying air stream such that an ideal pressure is maintained within the separator.
Clearly, the static pressure within the tangential separator is an important design consideration. Consider for the moment, a push type paper conveying and separation system where the paper material exits the separator and falls to a baler or compactor. If the static pressure at the material exit of the separator unit is too high, dust and paper scraps tend to swirl around the material exit resulting in a somewhat untidy and very dusty environment proximate the material exit. However, if the static pressure at the air and material inlet in the separator unit is too low, the result is an inefficient conveying system susceptible to clogging.
Pull type systems and hybrid type systems alleviate some of the aforementioned static pressure concerns but are generally more complex and more expensive systems. Moreover, the push type tangential separator systems are often the simplest to design, and are easy to install and maintain.
One related art tangential air separator is disclosed in U.S. Pat. No. 4,900,345 issued to Le Jeune which discloses the use of a deformed cylindrical grid in a tangential separator which allows most of the air flow to exit tangentially through the separator. The remainder of the air together with the transported objects presumably exit through a central exit portion of the separator via the spiral nature of the deformed cylindrical grid.
Another related art tangential separator system is disclosed in U.S. Pat. No. 4,300,926 issued to Brooks which discloses a separation apparatus adapted to receive a stream of airborne material and which includes a single rear exit screen and a bottom material exit. An adjustable baffle is located near the separator inlet directing the incoming stream to the rear exit screen which allows the air to exit tangentially while the material continues to be transported through separator. The separator is designed with an increasing cross-sectional area for decelerating the transported material as it moves through the duct.
Still another related art system is disclosed in U.S. Pat. No. 4,484,843 issued to McGlinsky et al. which shows a multi-chamber pneumatic conveying scrap paper system that also utilizes a flat rear exit screen for passing air and dust while the paper is directed and/or falls downward to a gathering hopper.
While these related art systems may adequately separate the transported material from the air stream, there remains a need to provide an improved tangential separator that is relatively small device, yet simple to install, operate and maintain and more importantly facilitates the relatively clean discharge of material.